Two years earlier, Caroline had delivered a stillborn baby and their only focus was on bringing into the world a healthy child.

But families change quickly. The couple formed six embryos and the first one they implanted was successful. Not long after their son turned one, Caroline fell pregnant naturally, and within three years of starting IVF treatment their family was complete. Five embryos were waiting on ice.

''Since my daughter was born, we've been saying we really need to start thinking about them,'' Caroline said. ''Every six months we've had to pay for storage and it just keeps reminding you, 'We have to make a decision on this'.''

A report on frozen embryos from the University of Technology, Sydney, found many couples anticipated embryo destruction as an emotional event and the ''least worst'' of the options available.

Caroline and Joseph decided they didn't want to discard their unused embryos. They wanted to donate them to an infertile couple, but the option was not available at their clinic. So they moved their embryos to IVF Australia, which does offer donation, but it took them a while to be comfortable with the possibility of someone else raising their genetic offspring.

''I'm not religious by any means but I would rather these embryos have a chance to be with a good family than nothing,'' Caroline said. ''And if … these children, or child, want to knock on our door … we will see them as nieces and nephews rather than children, because they are someone else's children.''